The present invention relates to switching power supplies, in particular to switching power supplies suitable for driving a load where a load current may abruptly vary.
Conventionally, a so-called DC-to-DC converter is known as a switching power supply. A representative DC-to-DC converter converts DC input into AC output by using a switching circuit, then transforming (performing step-up or step-down) the resulting AC output by the use of a transformer. It then converts the AC output to a DC output by the use of an output circuit thus obtaining a DC output different from the input voltage.
In such switching power supply, output voltage is detected by a control circuit, and the switching operation is controlled by a switching circuit based on the detected output voltage. This supplies a stable operating voltage to a load that is to be driven by the switching power supply.
When a load is driven where the load current (output current at the switching power supply) abruptly changes, switching power supplies of related art have difficulties in maintaining a stable output voltage.
In particular, a CPU (Central Processing Unit) or a DSP. (Digital Signal Processor) has, in the active state, a low operating voltage with high current while a small current in the inactive state. Thus, in existing switching power supply, an abrupt change in the output current could cause a large change in the output voltage. The CPU or DSP is a device featuring very high-speed operation so that a change in the output voltage may cause malfunction unless the output voltage is stabilized without delay.
This invention is to provide a switching power supply suitable for driving the load where load current may change abruptly.
Another object of the invention is to provide a switching power supply where a change in the output voltage caused by an abrupt change in the output current is reduced.
At last, the invention is to provide a switching power supply that can effectively detect the abrupt change in the output current.
The switching power supply in this invention comprises: a main circuit having a switching circuit for converting the DC input voltage to an AC voltage, an output circuit for rectifying the AC voltage to generate a DC output voltage; a control circuit for controlling the operation of the main circuit; an abrupt load change detector circuit for detecting an abrupt change in the load current supplied from the main circuit, the abrupt load change detector circuit including the first filter and the second filter for receiving the output voltage, and a detection signal generating means for generating an abrupt load change detection signal based on the outputs of the first filter and the second filter.
According to the invention, an abrupt change in the load current supplied from the main circuit is detected based on the outputs of the first filter and the second filter receiving the output voltage. This eliminates a power loss or operation delay caused when a resistor or a current transformer is used to directly detect the output current. Proper use of an abrupt load change detection signal allows dramatic improvement in transient response.
In the preferable embodiment of the invention, the time constant of the first filter and the second filter differ from each other.
In a further preferred embodiment of the invention, the first filter and the second filter are either a low-pass or a high-pass filter.
In a further preferred embodiment of the invention, the detection signal generating means is comprised of a comparator for receiving the output of the first filter at one input terminal and the output of the second filter at the other input terminal.
In a further preferred embodiment of the invention, in normal state, the output voltage levels of the first filter and the second filter differ from each other.
In another preferred embodiment of the invention, the detection signal generating means is comprised of an operational amplifier for amplifying the output voltage level difference between the first filter and the second filter and of a comparator for activating the abrupt load change detection signal in response to the output of the operational amplifier exceeding a predetermined threshold voltage.
According to the preferred embodiment of the invention, the operational amplifier for amplifying the output voltage level difference between the first filter and the second filter makes it is possible to detect the abrupt load change state more accurately and steadily.
In another preferred embodiment of the invention, the predetermined threshold voltage is associated with the output voltage.
According to the preferred embodiment of the invention, it is not necessary to change the control in the abrupt load change detector circuit even when the target voltage for the output voltage is changed.
In another preferred embodiment of the invention, the output voltage level of the first filter in normal state is substantially equal to that of the second filter.
In another preferred embodiment of the invention, the control circuit has at least an amplifier for receiving the output voltage or a voltage associated with the output voltage at its input terminal and the abrupt load change detector circuit comprises a means for varying the level at the input terminal of the amplifier in response to the activation of the abrupt load change detection signal.
According to the preferred embodiment of the invention, since it is possible to promptly recover from an abrupt change in the output voltage caused by an abrupt change in the load state, there is a dramatic improvement in transient response. This effectively prevents malfunction of the load caused by a change in the supply voltage even when a CPU or DSP is the load.
In another preferred embodiment of the invention, the control circuit has a variable amplifier that receives, at its input terminal, the output voltage or a voltage associated with the output voltage. The circuit has a variable amplifier where it switches the characteristics based on the abrupt load change detection signal.
According to the preferred embodiment of the invention, since it is possible to promptly recover from an abrupt change in the output voltage caused by an abrupt change in the load state, a dramatic improvement in transient response can be seen.
In another preferred embodiment of the invention, the control circuit comprises several amplifiers having different characteristics for receiving, at its respective input terminals, the output voltage or a voltage associated with the output voltage, several PWM control circuits for generating corresponding control signal groups based on the outputs of the corresponding amplifiers, and a selector for choosing one of the control signal groups based on the abrupt load change detection signal, thereby controlling the operation of the main circuit based on the selected control signal group.
According to the preferred embodiment of the invention, it is possible that by promptly recovering from an abrupt change in the output voltage caused by an abrupt change in the load, dramatic improvements in transient response can be seen.
In another preferred embodiment of the invention, the control circuit comprises at lease several amplifiers having different characteristics for receiving at its respective input terminals, an output voltage or a voltage associated with the output voltage, a selector for choosing one of the outputs of several amplifiers based on the abrupt load change detection signal, and a PWM control circuits for generating control signal groups based on the selected output, thereby controlling the operation of the main circuit based on the control signal group.
According to the preferred embodiment of the invention, it is possible that by promptly recovering from an abrupt change in the output voltage caused by an abrupt change in the load state, dramatic improvement in transient response can be seen.
In another preferred embodiment of the invention, the control circuit forcefully places the output circuit of the main circuit in a synchronous rectification state or in a halt state of synchronous rectification in response to the abrupt load change detection signal being active.
According to the preferred embodiment of the invention, it is possible that by promptly recovering from an abrupt change in the output voltage caused by an abrupt change in the load state, dramatic improvement in transient response can be seen.
In another aspect, the switching power supply invented comprises: a main circuit having a switching circuit for converting the DC input voltage to an AC voltage, an output circuit for rectifying the AC voltage to generate a DC output voltage; a control circuit for controlling the operation of the main circuit; an abrupt load change detector circuit for detecting an abrupt change in the load current supplied from the main circuit, an abrupt load change detector circuit which includes the first, second and third filters for receiving the output voltage, the first comparator for receiving both the output of the first filter at one input terminal and the output of the second filter at the other input terminal which generates abrupt load change detection signal 1 based on these outputs and the second comparator for receiving the output of the first filter at one input terminal and the output of the third filter at the other input terminal which generates abrupt load change detection signal 2 based on these outputs.
According to the invention, since the first comparator for generating abrupt load change detection signal 1 and the second comparator for generating abrupt load change detection signal 2 are used, proper setting of the characteristics of the first, second and third filters allows detection of the abrupt load change state (for example an abrupt increase in load) in one direction as well as the abrupt load change state in the opposite of the one direction(for example an abrupt drop in load). Proper setting of the characteristics of the first, second and third filters also allows detection that is dependent on the degree of abrupt load change. By proper use of abrupt load change detection signals 1 and 2, it is possible to dramatically improve transient response.
In a preferred embodiment of the invention, the output voltage levels of the first filter and the second filter in normal state differ from each other, and the output voltage levels of the first and third filters in normal state also differ from each other.
In a further preferred embodiment of the invention, the control circuit has at least an amplifier for receiving, at its input terminal, the output voltage or a voltage associated with the output voltage, and the abrupt load change detector circuit includes means for varying the level at the input terminal of the amplifier in one direction in response to the activation of abrupt load change detection signal 1 and varying the level at the input terminal of the amplifier in the opposite of the one direction in response to the activation of abrupt load change detection signal 2.
According to the preferred embodiment of the invention also, it is possible to promptly recover from an abrupt change in the output voltage caused by an abrupt change in the load state, which dramatically improves transient response.
A switching power supply of the third aspect of the invention comprises: a main circuit having a switching circuit for converting the DC input voltage to an AC voltage, an output circuit for rectifying the AC voltage to generate a DC output voltage; a control circuit for controlling the operation of the main circuit; an abrupt load change detector circuit for detecting an abrupt change in the load current supplied from the main circuit, the abrupt load change detector circuit that includes the first filter and the second filter for receiving the output voltage, an operational amplifier for amplifying the output voltage level difference between the first filter and the second filter, the first comparator for activating the abrupt load change detection signal 1 in response to the output of the operational amplifier when threshold voltage 1 is exceeded, and the second comparator for activating abrupt load change detection signal 2 in response to the output of the operational amplifier when threshold voltage 2 is exceeded.
According to the invention, since the first comparator for generating abrupt load change detection signal 1 and the second comparator for generating abrupt load change detection signal 2 are used, proper setting of the threshold voltages of the first filter and the second filter allows detection of the abrupt load change state (for example an abrupt increase in load) in one direction as well as the abrupt load change state in the opposite of the one direction (for example an abrupt drop in load). Proper setting of the threshold voltages of the first filter and the second filter also allows detection that is dependent on the degree of abrupt load change. By proper use of abrupt load change detection signals 1 and 2, it is possible to dramatically improve transient response.
In a preferred embodiment of the invention, both threshold voltages 1 and 2 are associated with the output voltage.
In another preferred embodiment of the invention, it is not necessary to change the control in the abrupt load change detector circuit even when the target voltage for the output voltage is changed.
In a further preferred embodiment of the invention, threshold voltage 1 is lower than the output level of the operational amplifier in normal state and threshold voltage 2 is higher than the output voltage level of the operational amplifier in normal state.
In a further preferred embodiment of the invention, it is possible to detect the abrupt load change state (for example an abrupt increase in load) in one direction as well as the abrupt load change state in the opposite of the one direction (for example an abrupt drop in load).
In a further preferred embodiment of the invention, the control circuit has at least an amplifier that receives, at its input terminal, the output voltage or a voltage associated with the output voltage, and the abrupt load change detector circuit includes means for varying the level at the input terminal of the amplifier in one direction in response to activation of abrupt load change detection signal 1 and varying the level at the input terminal of the amplifier in the opposite of the one direction in response to activation of abrupt load change detection signal 2.
According to the preferred embodiment of the invention, it is possible to promptly recover from an abrupt change in the output voltage caused by an abrupt change in the load state, which dramatically improves transient response.
In a further preferred embodiment of the invention, threshold voltages 1 and 2 are either lower or higher than the output voltage level of the operational amplifier in normal state.
In a further preferred embodiment of the invention, it is possible to perform detection that is dependent on the degree of abrupt load change.
In a further preferred embodiment of the invention, the control circuit has at least an amplifier that receives, at its input terminal, the output voltage or a voltage associated with the output voltage and the abrupt load change detector circuit including means for varying the level at the input terminal of the amplifier at rate 1 in one direction in response to activation of abrupt load change detection signal 1 and varying the level at the input terminal of the amplifier at a rate 2 in response to activation of abrupt load change detection signal 2.
According to the preferred embodiment of the invention, it is possible to promptly recover from an abrupt change in the output voltage caused by an abrupt change in the load, which dramatically improves transient response.